The weather conditions were appropriate for the flight. The flight instructor was qualified and had experience appropriate to the flight being conducted. Although the minimum altitude recovery of 4 000 feet agl recommended by the manufacturer was not followed by all the flight instructors at Laurentide Aviation, it is likely that a higher altitude would not have enhanced the flight instructor's chances of recovery from the spin in this occurrence. However, the failure to follow specified altitude restrictions for spin exercises increases the risk of such operations and deserves attention by Transport Canada by means of reminding operators of such safety precautions. It was presumed that the lack of a rudder bar return spring would not affect the flight operations of the aircraft, and the aircraft was released for flight. In reality, because the spring was missing, the aircraft was not airworthy. Further, the required entries were not made in either the snag book or the journey logbook. Had the logbooks reflected the defect and been available to the pilots, the flight instructor likely would have been aware that the rudder bar return spring was missing and would have had the option of refusing to operate the aircraft in that condition. There was no communication from the maintenance personnel to the flight crew member about the maintenance actions taken on the aircraft in relation to the rudder system. The requirement to conduct independent inspections is intended to provide a further check of an engine or flight control system which has been disturbed during maintenance. The objective is to increase the likelihood that the system is going to operate properly. Work was done on the flight control system in the form of inspection, removal of broken parts, discussion, and decision making. The absence of the rudder bar return spring and its attachment bracket arguably resulted in a disturbance to the flight control system which ought to have required an independent inspection. No independent check was completed and Transport Canada maintains that this is not required in these circumstances because no work was done on the rudder control system. In any event, the removal of the rudder return spring meant that the flight authority was no longer valid because the aircraft no longer conformed to its type certification. During the maintenance audit of the flight school operator at Saint-Hubert Airport, discrepancies were noted that led to the grounding of several aircraft, including five Cessna 152 aircraft with reported rudder over-traveling. The audit revealed that there were scratches or score marks on the five airplanes that indicated that the rudder horns had over-traveled above and beyond the stop bolt at some time. The preliminary findings regarding rudder over-traveling led to additional examinations and tests by the TSB, Transport Canada, Cessna, and Laurentide Aviation personnel on 22 February 2000. The tests conducted on 22 February 2000 revealed that, under certain conditions, the rudder can over-travel and jam in an irreversible condition, exactly like the condition of the rudder found on the accident aircraft. A full up, or nearly full up, elevator and a full rudder input are the control inputs used for spin entry. The implications of removing the broken rudder bar return spring from the accident aircraft were not apparent to the Laurentide Aviation maintenance personnel. However, the recent examinations and tests confirmed that the absence of the return spring, in combination with other factors such as incorrect rudder rigging, condition of the rudder, and rudder horn or stop plate condition and alignment, set the stage for irreversible jamming of the rudder during application of controls for spin entry. It can therefore be concluded that the aircraft entered a left spin with the rudder locked at a 34-degree deflection. With the rudder jammed the way it was, no amount of right rudder pedal force would have released the jammed rudder, as the direction of cable pull tends to increase the jamming by closing the horn. The actions proposed by Cessna to design a new rudder horn stop bolt assembly should provide protection against future jamming of the rudder--if the new design is installed on the aircraft. However, the Service Bulletin planned to offer the new configuration will not be mandatory without regulatory airworthiness actions.Analysis The weather conditions were appropriate for the flight. The flight instructor was qualified and had experience appropriate to the flight being conducted. Although the minimum altitude recovery of 4 000 feet agl recommended by the manufacturer was not followed by all the flight instructors at Laurentide Aviation, it is likely that a higher altitude would not have enhanced the flight instructor's chances of recovery from the spin in this occurrence. However, the failure to follow specified altitude restrictions for spin exercises increases the risk of such operations and deserves attention by Transport Canada by means of reminding operators of such safety precautions. It was presumed that the lack of a rudder bar return spring would not affect the flight operations of the aircraft, and the aircraft was released for flight. In reality, because the spring was missing, the aircraft was not airworthy. Further, the required entries were not made in either the snag book or the journey logbook. Had the logbooks reflected the defect and been available to the pilots, the flight instructor likely would have been aware that the rudder bar return spring was missing and would have had the option of refusing to operate the aircraft in that condition. There was no communication from the maintenance personnel to the flight crew member about the maintenance actions taken on the aircraft in relation to the rudder system. The requirement to conduct independent inspections is intended to provide a further check of an engine or flight control system which has been disturbed during maintenance. The objective is to increase the likelihood that the system is going to operate properly. Work was done on the flight control system in the form of inspection, removal of broken parts, discussion, and decision making. The absence of the rudder bar return spring and its attachment bracket arguably resulted in a disturbance to the flight control system which ought to have required an independent inspection. No independent check was completed and Transport Canada maintains that this is not required in these circumstances because no work was done on the rudder control system. In any event, the removal of the rudder return spring meant that the flight authority was no longer valid because the aircraft no longer conformed to its type certification. During the maintenance audit of the flight school operator at Saint-Hubert Airport, discrepancies were noted that led to the grounding of several aircraft, including five Cessna 152 aircraft with reported rudder over-traveling. The audit revealed that there were scratches or score marks on the five airplanes that indicated that the rudder horns had over-traveled above and beyond the stop bolt at some time. The preliminary findings regarding rudder over-traveling led to additional examinations and tests by the TSB, Transport Canada, Cessna, and Laurentide Aviation personnel on 22 February 2000. The tests conducted on 22 February 2000 revealed that, under certain conditions, the rudder can over-travel and jam in an irreversible condition, exactly like the condition of the rudder found on the accident aircraft. A full up, or nearly full up, elevator and a full rudder input are the control inputs used for spin entry. The implications of removing the broken rudder bar return spring from the accident aircraft were not apparent to the Laurentide Aviation maintenance personnel. However, the recent examinations and tests confirmed that the absence of the return spring, in combination with other factors such as incorrect rudder rigging, condition of the rudder, and rudder horn or stop plate condition and alignment, set the stage for irreversible jamming of the rudder during application of controls for spin entry. It can therefore be concluded that the aircraft entered a left spin with the rudder locked at a 34-degree deflection. With the rudder jammed the way it was, no amount of right rudder pedal force would have released the jammed rudder, as the direction of cable pull tends to increase the jamming by closing the horn. The actions proposed by Cessna to design a new rudder horn stop bolt assembly should provide protection against future jamming of the rudder--if the new design is installed on the aircraft. However, the Service Bulletin planned to offer the new configuration will not be mandatory without regulatory airworthiness actions. During a practice spin exercise, the rudder locked in a full left deflection, which could not be overcome by the crew. The aircraft was released for flight with a rudder bar return spring missing, which, in combination with other factors, probably allowed the rudder to lock in a full left deflection. Tests conducted on an aircraft similar to the accident aircraft showed that the design and condition of the stop bolt and rudder horn stop plate allowed the stop plate to over-travel the stop bolt and jam. Because the direction of cable pull tends to close the mouth of the horn, increasing the jamming effect, applying right rudder force would only have tightened the jam rather than broken it.Findings as to Causes and Contributing Factors During a practice spin exercise, the rudder locked in a full left deflection, which could not be overcome by the crew. The aircraft was released for flight with a rudder bar return spring missing, which, in combination with other factors, probably allowed the rudder to lock in a full left deflection. Tests conducted on an aircraft similar to the accident aircraft showed that the design and condition of the stop bolt and rudder horn stop plate allowed the stop plate to over-travel the stop bolt and jam. Because the direction of cable pull tends to close the mouth of the horn, increasing the jamming effect, applying right rudder force would only have tightened the jam rather than broken it. The aircraft was released for flight with a rudder bar return spring missing, and without the required documentation being entered in the journey logbook and technical logbook regarding the missing spring and the work performed on the rudder system. Thus, the aircraft did not meet the airworthiness requirements for flight. Laurentide Aviation maintenance personnel released an aircraft for flight in an unsafe condition. No entry was made in the aircraft journey logbook or technical logbook indicating that a rudder bar return spring was missing from the aircraft, and the flight instructor was unaware that the spring was missing. Routinely, the company was using a snag book to keep records of discrepancies and repairs instead of making the required entries in the journey logbook and in the technical logbook. This method of recording was not approved by Transport Canada, nor was it in accordance with the company's Maintenance Control Manual (MCM) and Maintenance Policy Manual (MPM). Tests conducted on 22 February 2000 confirmed that, under certain conditions, the rudder will jam at full deflection.Other Findings Related to Risks to Persons, Property and the Environment The aircraft was released for flight with a rudder bar return spring missing, and without the required documentation being entered in the journey logbook and technical logbook regarding the missing spring and the work performed on the rudder system. Thus, the aircraft did not meet the airworthiness requirements for flight. Laurentide Aviation maintenance personnel released an aircraft for flight in an unsafe condition. No entry was made in the aircraft journey logbook or technical logbook indicating that a rudder bar return spring was missing from the aircraft, and the flight instructor was unaware that the spring was missing. Routinely, the company was using a snag book to keep records of discrepancies and repairs instead of making the required entries in the journey logbook and in the technical logbook. This method of recording was not approved by Transport Canada, nor was it in accordance with the company's Maintenance Control Manual (MCM) and Maintenance Policy Manual (MPM). Tests conducted on 22 February 2000 confirmed that, under certain conditions, the rudder will jam at full deflection. Safety Action Action Taken On 14 March 2000, Cessna notified the TSB that it had designed a rudder horn stop bolt with a larger head diameter to prevent over-travel of the rudder following a hard rudder input. Cessna has notified the Federal Aviation Administration (FAA) Aircraft Certification Office about this matter and expects to issue a Service Bulletin offering the new configuration rudder stop bolt for all Cessna 150s and 152s built after 1966. A time frame for these actions was not specified. On 09 May 2000, Transport Canada issued Service Difficulty Alert (SDA) No. AL-2000-04 following information gathered during the tests carried out at Saint-Hubert on 22 February 2000. The SDA discusses the accident circumstances and outlines details regarding the inspection of the rudder control system. Action Required While stated action by Cessna to develop a Service Bulletin designed to prevent over-travel of the rudder is appropriate, the Board is concerned that, since the proposed Service Bulletin will be voluntary, not all Canadian-registered Cessna 150s and 152s will be modified. Therefore, the Board recommends that: Any mandatory airworthiness actions to retrofit Cessna 150 and 152 aircraft with newly designed rudder horn stop bolt systems will likely take considerable time to complete. In the meantime, these aircraft will be flying with a known safety deficiency. The circumstances of this accident suggest that the serious implications of the broken or missing rudder cable return spring were not fully understood. Moreover, the possibility of an irreversibly jammed rudder during intentional spin entry by full rudder deflection was not understood until this accident investigation was completed. Therefore, the Board recommends that: The required logbook entries regarding the maintenance performed on the rudder system were not made, and it was evident that the operator, in general, did not maintain the aircraft journey logbooks in accordance with the Canadian Aviation Regulations (CARs). Therefore, the Board recommends that: The FAA, as the regulatory body in the state of design and manufacture, has primary responsibilities with regard to continuing airworthiness of both the Cessna 150 and 152 aircraft. Therefore, the Board recommends that: